Field of the Invention
The present invention relates to a backlight driver of a liquid crystal display device, and more particularly, to a backlight driver of a liquid crystal display device and a method for driving the same so as to prevent backlight flicker by properly filtering an input pulse width modulation (PWM) signal.
Discussion of the Related Art
Representative examples of a flat panel display apparatus for displaying an image using digital data include a liquid crystal display (LCD) device using liquid crystal, a plasma display panel (PDP) using discharge of inert gas, a organic light emitting diode (OLED) display device using an OLED, and the like. Among these, the LCD device has been widely used in various application fields such as in a television (TV), a monitor, a laptop computer, and a portable phone.
An LCD device displays an image through a pixel matrix using the electrical and optical properties of liquid crystals having anisotropic properties with respect to refractive index, dielectric constant, and the like. Each pixel of the LCD device implements a gray level by adjusting optical transmittance with respect to a polarization plate using variation in liquid crystal orientation direction according to a data signal. The LCD device includes a liquid crystal panel for displaying an image through the pixel matrix, a drive circuit for driving the liquid crystal panel, a backlight unit for irradiating light to the liquid crystal panel, and a backlight driver for driving the backlight unit.
The backlight driver for drive of the backlight unit controls the brightness of the backlight unit by adjusting on/off time of the backlight unit according to a duty ratio of a pulse width modulation (PWM) signal input from a TV set or a timing controller.
In this case, the backlight driver detects the duty ratio of the input PWM signal and reflects the detected duty ratio to a vertical synchronization signal input from a timing controller to generate and use an output PWM signal for control of the backlight unit in order to drive the backlight unit according to the liquid crystal panel.
However, since there occurs a specific period in which a duty ratio becomes unstable when a frequency of an input PWM signal is changed, the duty ratio of the output PWM signal is changed, resulting in backlight flicker.
For example, if a frequency of the input PWM signal having the duty ratio of 10% is changed from 60 Hz to 50 Hz as exemplarily shown in FIG. 1, there may occur a specific period having an unstable duty ratio of 8.35% during the frequency change process. In this case, the unstable duty ratio is reflected in the output PWM signal without change so as to change backlight luminance, resulting in the occurrence of image quality deterioration such as flicker on the screen.